WOx/ZrO2 catalysts Part 1. Preparation, bulk and surface characterization

Zirconia supported tungsten oxide catalysts (tungsten content up to 33.7 wt.%) were prepared by equilibrium adsorption and impregnation in acid (pH 2.7) and basic (pH 10) conditions using hydrous zirconium oxide. After thermal treatment at 1073 K in air, the catalysts were characterized by surface area determination, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS). diffuse optical reflectance, Raman spectroscopy and chemical analysis. The results show that tungsten is present as a dispersed phase and as monoclinic WO3 crystallites, The density of tungsten in a dispersed form was estimated as about 5 atoms nm(-2). Leaching treatments with ammonia revealed that only a fraction of the dispersed tungsten interacts directly with the support surface. The interacting species, in the form of small clusters, as revealed by EXAFS and Raman spectroscopy, control the ZrO2 surface area and are responsible for the structural changes in the support. Subsequent thermal treatment up to 1073 K in air leaves them unchanged. (C) 2002 Elsevier Science B.V. All rights reserved